Driving Rod For The Piston Of A Reciprocating Compressor

ABSTRACT

A driving rod for the piston of a reciprocating compressor of the type that comprises: a cylinder block defining a compression chamber; a piston reciprocating within the compression chamber; a driving means to apply reciprocating forces to the piston; and a driving rod disposed between the piston and the driving means and comprising a number, greater than 1, of rods disposed side by side along the axis of the driving rod and each presenting a cross-section that is dimensioned and configured to impart to the driving rod, jointly with the other rods, a required axial rigidity and a flexibility, in at least one direction transversal to the axis of the driving rod, sufficient to absorb, at least substantially, the forces exerted on the piston by the driving rod and by the driving means.

FIELD OF THE INVENTION

The present invention refers to a driving rod to be applied to areciprocating compressor with an electric motor of the rotary or lineartype, said driving rod being constructed to operatively couple a drivingmeans to a piston to be reciprocated in the interior of a compressionchamber of the compressor, according to the axis of said chamber.

PRIOR ART

The reciprocating compressors that are driven by a rotary or linearelectric motor generally comprise a cylinder block defining, internally,a compression chamber inside which axially reciprocates a piston coupledto a driving means mounted to the cylinder block and operativelyassociated with the electric motor of the compressor.

The piston is coupled to the driving means so as to allow forces to betransferred therebetween and to make the piston move inside thecompression chamber according to an axial direction coinciding with theaxis of said compression chamber in order to minimize the transversalreaction forces of the cylinder block against the piston inside thecompression chamber. As known, the transversal reaction forces of thecylinder block against the piston can provoke excessive friction betweenthe piston and the cylinder block, leading to an increase of energyconsumption, consequently reducing the efficiency of the compressor, andto an accelerated wear of the components submitted to high frictionlevels, reducing the useful life of the compressor.

A known reciprocating compressor with a linear electric motor, asillustrated in FIG. 1 of the appended drawings, comprises a cylinderblock 10 defining, internally, a compression chamber 11 presenting anaxis 12 and with a piston 20 axially reciprocating therewithin. Thecompression chamber 11 has an end that is generally closed by a valveplate 13 and by a cylinder head 14, the valve plate 13 being providedwith a suction valve 13 a and a discharge valve 13 b of adequateconstruction to control the admission and discharge of gas in relationto the compression chamber 11 upon the movement of the piston 20.

In the known construction illustrated in FIG. 1, the piston 20 isoperatively coupled to a driving means DM, which in the case of acompressor with a linear electric motor, comprises an actuator 30 in theform of a tubular structure, concentric and external to the compressionchamber 11 and carrying a magnetic element 31 to be operativelyimpelled, with the actuator 30, upon the energization of a linearelectric motor 40 mounted to the cylinder block 10 around thecompression chamber 11. In this example, the driving means furthercomprises a set of springs 60 mounted between the cylinder block 10 andthe piston 20.

To the piston 20 is directly or indirectly coupled an end of a drivingrod 50 whose opposite end is coupled to the springs 60, helical springsfor example, which are mounted in such a way as to exert opposite axialforces on the piston 20 upon its axial reciprocating movement in theinterior of the compression chamber 11 provoked by the driving means DMcomprising the actuator 30 and the springs 60. The piston 20, theactuator 30 and the springs 60 form the resonant assembly of thecompressor with a linear motor.

These compressors are designed and constructed so that the axis of theaxial reciprocating movement of the piston 20 coincides with the axes ofboth the piston 20 and the compression chamber 11, aiming at minimizingor even suppressing the transversal reaction forces between the piston20 and the cylinder block 10. However, in use, said axes can becomemisaligned and thus undesirable transversal reaction forces may occurbetween the piston 20 and the cylinder block 10 by reason of someconstructive characteristics inherent to the compressors, such as thegeometrical errors in the construction of the helical springs and thetransversal rigidity thereof when they are axially and elasticallydeformed.

Besides the aspects above, one should consider the fact thatmisalignments commonly occur in the construction and assembly ofmechanical components, as perfection is not usually reached in terms ofdimensions and forms of the different components of a mechanical device.

In the construction illustrated in FIG. 1, the driving rod 50 has theform of a generally tubular and transversally rigid axial rod, wherebythe piston-actuator assembly behaves as a single body onto which areapplied magnetic axial forces of the linear motor 40 which do notproduce, over the piston 20, transversal components capable of causingexcessive friction between said piston 20 and the cylinder block 10.

However, the springs 60 exert over the piston-actuator assembly, notonly the axial forces resulting from the compression thereof during themovement of the piston 20, but also transversal forces whose intensityvaries as a function of the errors of construction and assembly of thesprings 60. Such undesirable transversal forces, produced by theoperational deformation of the springs, tend to misalign the piston 20in relation to the axis of the compression chamber 11, giving rise totransversal reaction forces of the cylinder block 10, as well as aconsequent higher friction between the latter and the piston 20 axiallyreciprocating within the compression chamber 11.

U.S. Pat. No. 5,525,845, from Sumpower Inc., describes a constructivesolution for the problem cited above, according to which the drivingrod, which can be mounted in different manners between the piston andthe driving means, is constructed so as to present a required axialrigidity and also a transversal flexibility sufficient to prevent allthe transversal forces acting on the piston, including the force exertedby the driving rod itself, from surpassing the centralizing transversalforces applied to the piston by a pneumatic bearing provided between thelatter and the cylinder block.

This prior solution uses a single-piece driving rod dimensioned topresent the necessary axial rigidity and a transversal flexibility in adegree compatible with the centralizing transversal forces produced onthe piston by the pneumatic bearing. Said prior art solution do notpermit an adequate flexibility in the dimensioning of the driving rod inrelation to compressors in which the axial force to be transmitted orsupported by the driving rod requires a cross-section area for thelatter which hinders, in the length available for the single-piecedriving rod, the latter from presenting the desired transversalflexibility. The use of multiple rods is suggested (FIG. 8) only in aspaced-apart relationship, each rod being dimensioned to present thedesired characteristics of axial rigidity and transversal flexibility.This is a complex construction, requiring the provision of the pneumaticbearing to maintain the piston adequately centralized in the compressionchamber.

It should be further noted that the provision of multiple rods disposedspaced apart and symmetrical in relation to the axis of the compressionchamber, as suggested in FIG. 8 of U.S. Pat. No. 5,525,845, does noteliminate completely the deficiencies already discussed in relation tothe single-piece driving rod. The proposed prior arrangement provides aplurality of rods spaced from each other, connecting the set of flatsprings of a linear motor compressor with the structure that supportsthe cylinder block. These multiple rods can be dimensioned to provide,jointly, the necessary rigidity and the desired degree of flexibility inthe transversal direction. However, due to the fact of being spacedapart, said prior art multiple rods do not absorb transversal forcesproduced by angular misalignments of the axis of the driving means inrelation to the axis of the compression chamber. Such misalignments arenot absorbed by the spaced-apart rods, since the latter would have to beaxially deformed, partially by expansion and partially by construction.On the other hand, the required axial rigidity of the rods prevents themfrom being dimensioned to bend, reducing their length upon theoccurrence of said angular misalignments.

As illustrated in FIG. 2 of the appended drawings, the reciprocatingcompressors with a connecting rod-crankshaft mechanism driven by arotary motor also present problems related to geometrical and assemblyerrors. Such compressors also comprise a cylinder block 10 defining,internally, a compression chamber 11 with a reciprocating piston 20axially moving therewithin. The compression chamber 11 presents an axis12 and an end closed by a valve plate 33 provided with a suction valve13 a and a discharge valve 13 b, and a cylinder head 14.

In the compressor of the type illustrated in FIG. 2, the piston 20 isdriven by a driving means DM, in the form of a crankshaft 35, rotativelysupported in the cylinder block and mounted to a rotary motor (notillustrated), the crankshaft having an end receiving the larger eye of adriving rod 50 in the form of a connecting rod, whose smaller eye isrotatively supported on the known diametrical articulating pin 21 insidethe piston 20.

In the reciprocating compressors with a connecting rod-crankshaftmechanism, geometrical and assembly errors, as exaggeratedly illustratedin FIG. 2, can lead to the transmission of reaction forces FRtransversal to the axis 12 of the compression chamber 11, a situation inwhich the piston 20 tends to work misaligned with said axis 12. Thesereaction forces FR, acting mainly in the direction of the articulatingpin 21 of the piston 20, tend to produce undesirable levels of frictionbetween the piston 20 and the cylinder block 10, increasing theconsumption of energy in the operation of the compressor as well as thewear of the mutually frictional parts, reducing the reliability and theuseful life of the machine.

Also in this type of compressor, the solution taught by the prior art isto dimension the driving rod 50 with a cross-section which, in thelength defined in the compressor project, leads to the necessary axialrigidity of the driving rod, so that the latter can withstand thetransmission of forces between the driving means DM (crankshaft) and thepiston 20, but which however gives to the driving rod 50, in the form ofa connecting rod, a flexibility in a transversal direction whichminimizes the transmission of moment to the piston 20.

While being of low cost and easy to execute, said construction, asalready mentioned in relation to the driving rod of the linear motorcompressors, makes the dimensioning of the cross-section a problematictask due to the length limitations of the driving rod and to the degreeof transversal flexibility required to reduce the transmission ofmoments to the piston 20 to desirable levels.

SUMMARY OF THE INVENTION

Due to the dimensioning limitations of the cross-section of the drivingrods of the reciprocating compressors with a linear or rotary motor, itis the object of the present invention to provide a driving rodpresenting a construction that allows obtaining a flexibility, in atleast one transversal direction, as well as an axial rigidity which cancomply with the requirements of the compressor project regardless of thelength defined for the driving rod.

The driving rod proposed by the present invention offers a simplesolution that is easy to implement in the construction of reciprocatingcompressors, particularly those of the hermetic type used isrefrigeration systems of household electric appliances in which thepiston is designed to be axially displaced in a reciprocating movementinside a compression chamber, without being submitted to transversalreaction forces of the cylinder block caused by the acceptablegeometrical or assembly errors of the component parts involved, butwhich are sufficiently relevant to cause friction that abbreviates theuseful life of the compressor.

In order to attain the object cited above, the present driving rodcomprises a bundle of “n” rods arranged side by side along the axis ofthe driving rod, each rod presenting a cross-section that is dimensionedand configured to impart to the driving rod, jointly with the otherrods, an axial rigidity sufficient to transmit the reciprocating forcesbetween the driving means and the piston, and a flexibility, in at leastone transversal direction to the axis of the driving rod, sufficient toabsorb, at least substantially, the forces applied to the piston, insaid transversal direction, by both the driving rod and the drivingmeans in the region of the compression chamber.

According to the solution proposed by the invention, the number and thecross-section of the rods that form the driving rod can be defined toimpart to the latter optimized axial rigidity and transversalflexibility so that the reciprocating movement of the piston inside thecompression chamber of the cylinder block occurs with little or nofriction that abbreviates the useful life of the compressor.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below, with reference being made to theappended drawing, given by way of example of ways of carrying out theinvention and in which:

FIG. 1 is a schematic and simplified longitudinal sectional view of thecylinder block and the resonant assembly of a reciprocating compressordriven by a linear motor and in which the driving rod is constructedaccording to the prior art;

FIG. 2 is a schematic and simplified longitudinal sectional view of thecylinder block of a reciprocating compressor driven by a rotary motor,by a crankshaft and by a driving rod in the form of a connecting rodconstructed according to the prior art, with the piston beingexaggeratedly misaligned in the interior of the compression chamber;

FIG. 3 is a schematic and simplified longitudinal sectional view of thecylinder block and the resonant assembly of a reciprocating compressordriven by a linear motor and presenting a driving rod constructedaccording to the present invention;

FIG. 4 is a perspective view of driving rod formed by a plurality ofparallel rectilinear rods, with a circular cross-section and laterallyseated to each other;

FIG. 5 is a similar view to that of FIG. 4, but illustrating the rodsdisposed in a helical arrangement;

FIG. 6 is a rather schematic perspective view of a median portion of adriving rod formed by a plurality of rods surrounded by a sleeve in theform of an elastic ring;

FIG. 7 is a perspective view of the driving rod illustrated in FIG. 4,with the rods being surrounded by a sleeve in the form of a helicalspring;

FIG. 8 is a view similar to that of FIG. 7, but with the sleeve definedby a tube extension mounted around the rods of the driving rod;

FIG. 9 is a perspective view of a driving rod with the opposite end ofits rods being jointly affixed to respective terminal blocks;

FIG. 10 is a longitudinal sectional view of a terminal block insidewhich are mounted the respective ends of the rods of a partiallyillustrated driving rod;

FIG. 11 is an exploded perspective view of a driving rod formed bymultiple rods, with two end terminal blocks;

FIG. 12 is a longitudinal sectional view of the terminal blockillustrated in FIG. 11 and inside which are secured the respective endsof the rods of the partially illustrated driving rod;

FIG. 13 is a perspective exploded view of a terminal block and therespective end of a driving rod formed by multiple rods;

FIG. 14 is a perspective view of a driving rod formed by a plurality ofrods with a rectangular cross-section, with opposite ends being affixedto eyes to be respectively mounted to a piston and to a crankshaft ofthe compressor; and

FIG. 15 is a cross-sectional view of the driving rod illustrated in theprevious figure.

DETAILED DESCRIPTION OF THE INVENTION

As already mentioned, the construction of the driving rod of the presentinvention is designed to be applied to reciprocating compressors drivenby a linear motor or by a rotary motor.

FIG. 3 illustrates, basically, the same elements that constitute areciprocating compressor with a linear motor, contained in FIG. 1 andidentified by the same reference numbers, constructive differencesexisting only in relation to the construction and assembly of thedriving rod 50.

According to FIG. 3, the driving means DM is defined by an actuator 30and by a pair of springs 60, the actuator 30 comprising a basicstructure 30 a, transversal to the axis 12 of the compression chamber 11and incorporating an internal tubular projection 30 b, rigidly securedto the piston 20, and an external tubular projection 30 c that carriesthe magnetic element 31, the driving rod 50 being constructed so as tohave an end secured to the piston 20 and an opposite end secured to asupport 70 to which are mounted the adjacent ends of two springs 60,which in the illustrated construction have a helical form concentric tothe axis 12 of the compression chamber 11, the opposite ends of the twosprings 60 being mounted to the cylinder block 10, so that the springs60 can exert, over the support 70, opposite axial forces to betransmitted to the piston 20 by the driving rod 50 disposed accordingthe axis 12 of the compression chamber 11.

The support 70 can be constructed in different manners, but bearing inmind the necessity of its axial reciprocating movement, in conjunctionwith the piston 20 and with the adjacent ends of the springs 60, beingeffected with no interference of the driving means 30. In theillustrated exemplary construction, the support 70 comprises a pair ofshoes 71 disposed in planes that are parallel to each other, orthogonalto the axis 12 of the compression chamber 11 and located on oppositesides of the basic structure 30 a of the actuator 30, said shoes 71being axially interconnected by spacers 72 disposed through respectivewindows 33 provided in the basic structure 30 a of the actuator 30.

The exemplary construction illustrated in FIG. 3 makes the transversalforces produced by the springs 60, when the latter are elastically andaxially deformed, to have the tendency to be transferred to the piston20 through the driving rod 50.

According to the invention, in order to absorb the expected transversalforces produced by the springs 60, the driving rod 50 comprises a bundle“n” of rods 51 disposed side by side along the displacement axis of thepiston 20, each rod 51 presenting a cross-section that is dimensionedand configured to impart to the driving rod 50, jointly with the otherrods 51, an axial rigidity that is sufficient to transmit the axialforces to be applied to the piston 20 by the springs 60 upon movement ofthe actuator 30, as well as a flexibility, in at least one directiontransversal to the axis of the driving rod 50, which is sufficient toabsorb, at least substantially, the forces exerted over the piston 20,in said transversal direction, by the driving rod 50 and by the drivingmeans DM in the region of the compression chamber 11. The constructionof the driving rod 50 in the form of a bundle of rods 51 in an adequatematerial, usually steel, allows each rod 51 to be dimensioned with across-section area that corresponds to 1/n of a cross-section areanecessary to give to the driving rod 50, in the length determined inproject, an axial rigidity sufficient to withstand the requiredtransmission of axial forces between the piston 20 and the driving meansDM, which in the construction illustrated in FIGS. 3-13, comprises theactuator 30 and the springs 60.

Besides the characteristics above, the cross-section of the rods 51should be dimensioned and configured so that the sum of the moments ofinertia of the rods 51, in the determined transversal direction, is aninteger fraction of the moment of inertia, of said transversaldirection, of a single piece driving rod having a cross-section areacorresponding to the sum of the cross-section areas of the rods 51.

In the constructions illustrated in FIGS. 4-13, in which the rods 51present the same circular cross-section, the transversal flexibility ofthe driving rod 50 is equally achieved in any direction transversal tothe axis of said driving rod 50.

In the case of rods 51 with the same circular cross-section, the sum ofthe moments of inertia of the rods 51, in the axial direction,corresponds to a fraction “n” of the moment of inertia, in the sameaxial direction, of a single-piece driving rod 50 with its cross-sectionarea corresponding to the sum of the cross-section areas of the “n” rods51, as explained below, considering:

-   -   A1 as being the circular cross-section area of a single-piece        driving rod;    -   A2 as being the circular cross-section area of each of the rods        51 of a driving rod formed by a bundle of “n” rods 51;    -   K1 e K2 as being the transversal rigidity of the single-piece        driving rod and of each rod 51, respectively;    -   K2 res. as being the resultant transversal rigidity of the        bundle “n” of rods 51;    -   R1 e R2 as being the radiuses of the single-piece driving rod        and of the driving rod defined by multiple rods 51,        respectively; and    -   I as being the moment of inertia of each rod 51 in the        transversal direction.    -   Thus:

$A_{2} = {{\frac{A_{1}}{n}\pi \; R_{2}^{2}} = {{\frac{\pi \; R_{1}^{2}}{n}R_{2}} = {{\sqrt{\frac{R_{1}^{2}}{n}}{ou}\mspace{14mu} R_{2}} = \frac{R_{1}}{\sqrt{n}}}}}$

Rigidity (K) proportional to the moment of inertia

$(I) = {\frac{\pi \; R^{4}}{4} = \frac{\pi \; D^{4}}{64}}$K₁  proportional  R₁⁴${K_{2}\mspace{11mu} {proportional}\mspace{14mu} R_{2}^{4}} = {\left( \frac{R_{1}}{\sqrt{n}} \right)^{4}\mspace{14mu} {for}\mspace{14mu} a\mspace{14mu} {rod}}$${K_{2}{{res}.}} = {\sum\limits_{n}K_{2}}$${K_{2}{{res}.}} = {\frac{n \cdot R_{1}^{4}}{n^{2}} = \frac{R_{1}^{4}}{n}}$

Resulting

Thus, the transversal rigidity (K2 res.) of the bundle of “n” rods 51 ofcircular section will correspond only to a fraction “n” of thetransversal rigidity (K1) of a single-piece driving rod, with across-section area (A1) of the “n” rods 51 that form the bundle thatdefines the driving rod.

As illustrated in FIGS. 4, 5, 7, 8, 11 and 13, the rods 51 aresymmetrically disposed around the axis of the driving rod 50 and beingusually rectilinear and parallel to each other. In the constructionillustrated in FIG. 5, the rods 51 are provided in a helicalarrangement, symmetrically disposed in relation to said axis and aroundthe length of the driving rod 50.

In case the project of the driving rods 50 leads to a larger number “n”of thinner rods 51, i.e., with a reduced cross-section, one or more rods51 of the bundle of rods submitted to axial forces may be deformed,provoking collapse of the driving rod. In these cases, the rods 51 ofthe bundle can be jointly and medianly surrounded by one or more sleeves80, occupying part of the longitudinal extension of the driving rod 50.In FIG. 6, the sleeve 80 takes the form of an elastic ring 81, in ametallic of elastomeric material and dimensioned to press the rods

$\frac{K_{2}{{res}.}}{K_{1}} = {\frac{\frac{R_{1}^{4}}{n}}{R_{1}^{4}} = \frac{1}{n}}$${K_{2}{{res}.}} = \frac{K_{1}}{n}$

51, one against the others. In FIG. 7, the sleeve 80 is defined by ahelical spring 82, metallic or elastomeric and which is tightly mountedaround the bundle of rods 51 of the driving rod 50. In FIG. 8, thesleeve is defined by a tube extension 83, also made of any adequatematerial to impart to the driving rod 50 a certain transversalflexibility and which is mounted, with a small clearance, around thebundle of rods 51.

As illustrated in FIGS. 9-14, the rods 51 present opposite ends whichdefine the ends of the driving rod 50 and which are jointly secured inrespective terminal blocks 90 which may present different constructionsin different metallic or non-metallic materials;

In the case of the driving rods 50 applied to the compressors driven bylinear motors, the terminal blocks 90 are configured to define themounting means of the driving rod 50 in the piston 20 and in the support70 of the springs 60.

In the embodiment illustrated in FIGS. 9 and 10, each terminal block 90comprises a tubular body 91 that is usually externally threaded andincorporates an enlarged end head 91 a, preferably in the form of ahexagonal end nut turned to the rods 51 and presenting, internally, ahousing 91 b axially defined through the enlarged end head 91 a andthrough at least part of the length of the tubular body 91. Thisconstructive arrangement, also illustrated in FIG. 3, allows theterminal blocks 90 to have the tubular body 91 thereof threaded in acorresponding threaded orifice 23, 73 provided in the piston 20 and inthe support 70, respectively (FIG. 3). In the constructive arrangementillustrated in FIG. 10, the ends of the bundle of rods 51 are preferablytightly fitted and affixed by processes such as interference, welding,gluing, mechanical riveting or any other adequate process in theinterior of the housing 91 b of the respective tubular body 91.

In the embodiment of FIGS. 11 and 12, the terminal blocks 90 comprise anelongated body 92 externally threaded and incorporating an enlarged endhead 92 a. However, in this construction, the ends 52 of the rods 51 arelaterally curved, so that the terminal blocks 90 can be molded orinjected in aluminum, plastic or any other adequate material, directlyon said ends 52, guaranteeing the necessary mechanical anchorage betweenthe driving rod 50 and the terminal blocks 90. In the embodimentillustrated in FIG. 13, each terminal block is formed by a pair ofplates 93 to be secured to each other, sandwiching a respective end ofthe rods 51. One or both the plates 93 are internally provided with arecess 93 a configured to receive and fit a respective cross-sectionportion of an extension of the adjacent end of the bundle of rods 51,said extension being laterally curved or bent to facilitate locking theend of the driving rod 50 in each terminal block 90.

The plates 93 of each pair are preferably provided with orifices 93 bfor the passage of tightening screws (not illustrated).

As already mentioned above and illustrated in FIGS. 14 and 15, thedriving rod 50 can be designed in the form of a connecting rod tooperate in a reciprocating compressor of the type in which the piston 20is driven by a driving means DM in the form of a crankshaft 35 (see FIG.2). In this type of construction, the terminal blocks 90 of the drivingrod 50 are defined by eyes 94 to be respectively rotatively supportedaround the articulating pin 21 of both the piston 20 and the crankshaft35.

In the assemblies in which the actuator 30 is defined by a crankshaft35, the driving rod 50 comprises a number “n” of rectilinear parallelrods 51 which are laterally seated in relation to each other, each rod51 having a rectangular cross-section with a dimension L correspondingto a dimension “L” of the rectangular cross-section of a single-piecedriving rod and with the other dimension “h” corresponding to thefraction “n” of the other dimension “H” of the cross-section of saidsingle-piece driving rod. Thus, the same rectangular cross-section areaof each rod 51 corresponds to the fraction “n” of the cross-section areaof said single-piece driving rod. The same ratio is applied to therelation between the moment of inertia, in the axial direction of eachrod 51 and the moment of inertia in the axial direction of thesingle-piece driving rod. The sum of the cross-section areas of the rods51 corresponds to the cross-section area of said reference single-piecedriving rod. Thus, the driving rod 50 with “n” rods 51 has an axialrigidity equivalent to that obtained with the driving rod formed by onlyone rod having a cross-section area corresponding to the sum of thecross-section areas of the “n” rods 51 of the driving rod 50 withmultiple rods.

In the construction of FIGS. 14 and 15, in which the rods 51 have arectangular section, the moment of inertia of each rod 51 in thetransversal direction, parallel to the larger dimension “L”, correspondsto the moment of inertia, in the same direction, of a single-piecedriving rod with the same cross-section dimension “L”. It should benoted that the driving rod 50 is mounted so that said transversaldirection is orthogonal to the axis of the articulating pin 21 of thepiston 20. The articulation of the driving rod 50 to the piston 20allows the latter to stay in a coaxially aligned position in thecompression chamber 11, independently of the relative angularpositioning of the driving rod 50.

However, in the direction of the other dimension “h” of the rectangularcross-section of the rods 51, which direction is parallel and coplanarto the axis of the articulating pin 21 of the piston 20, the sum of themoments of inertia of the rods 51 in said other direction, orthogonal tothe anterior direction, corresponds to a fraction “n2” of the moment ofinertia, in the same transversal direction, of a single-piece drivingrod, with the corresponding cross-section dimension “L”, in the samedirection, being equal to the sum of the dimensions “h” of the rods 51in the same direction, as exposed below, and further considering:

-   -   A1 as being the rectangular cross-section area of a single-piece        driving rod;    -   A2 as being the rectangular cross-section area of each one of        the rods 51 of a driving rod formed by a bundle of “n” rods 51;    -   K1 e K2 as being the transversal rigidity of the single-piece        driving rod and of each rod 51 of the driving rod with “n” rods        51, respectively;    -   K2res. as being the resultant rigidity of the bundle of “n” rods        51, in said transversal direction; and    -   I1 e I2 as being the moments of inertia of the single-piece        driving rod and of each rod 51, in said transversal direction,        respectively.

Thus:

$A_{2} = {\frac{A_{1}}{n} = {{{L \cdot \frac{H}{n}}\mspace{14mu} e\mspace{14mu} h} = \frac{H}{n}}}$

Considering that the single-piece driving rod and the rods 51 of thedriving rod 50 with multiple rods present the same dimension “L” for thelarger side of the rectangular cross-section.

${{{Rigidity}(K)}\mspace{14mu} {proportional}\mspace{14mu} I} = \frac{L{\cdot h^{3}}}{12}$$I_{1} = {{\frac{L \cdot H^{3}}{12}\mspace{14mu} e\mspace{14mu} I_{2}} = {\frac{L \cdot h^{3}}{12} = {\frac{L}{12} \cdot \frac{H^{3}}{n^{3}}}}}$${K_{2}{{res}.}} = {{\sum\limits_{n}{K_{2}\mspace{14mu} {proportional}\mspace{14mu} {n \cdot I_{2}}}} = {n \cdot \frac{L}{12} \cdot \frac{H^{3}}{n^{3}}}}$resulting$\frac{K_{2}{{res}.}}{K_{1}} = {\frac{\frac{L}{12} \cdot \frac{H^{3}}{n^{2}}}{\frac{L}{12} \cdot H^{3}} = \frac{1}{n^{2}}}$${K_{2}{{res} \cdot}} = \frac{K_{1}}{n^{2}}$

Thus, the transversal rigidity (K2res.) of the bundle of “n” rods 51with a rectangular section will correspond only to a fraction “n2” ofthe transversal rigidity (K1) of a single-piece driving rod presenting across-section area (A1) corresponding to the sum of the cross-sectionareas (A2) of the “n” rods 51 that form the bundle that defines thedriving rod 50 of the invention, as well as a cross-section dimension“H”, in said direction, corresponding to the sum of the correspondingcross-section dimensions (h) of the rods 51 that form the driving rod50.

It should be understood that the bundle of rods 51 of the driving rod 50illustrated in FIGS. 14 and 15 could be surrounded by at least onesleeve 80 constructed according to any one of the forms described inrelation to FIGS. 6, 7 and 8.

1. A driving rod for the piston of a reciprocating compressor of thetype that comprises: a cylinder block defining, therewithin, acompression chamber; a piston axially reciprocating within thecompression chamber according to the axis of the latter; a driving meansmounted in the cylinder block to apply reciprocating forces to thepiston; and a driving rod coupled to the piston and to the drivingmeans, wherein the driving rod comprises a bundle of “n” rods disposedside by side along the axis of the driving rod, each rod presenting across-section that is dimensioned and configured to impart to thedriving rod, jointly with the other rods an axial rigidity sufficient totransmit the reciprocating forces to be applied to the piston, as wellas a flexibility, in at least one direction transversal to the axis ofthe driving rod, which is sufficient to absorb, at least substantially,the forces exerted on the piston, in said transversal direction, by thedriving rod and by the driving means in the region of the compressionchamber.
 2. The driving rod as set forth in clam 1, wherein each one ofthe rods present a cross-section area corresponding to 1/n thecross-section area needed to impart to the driving rod the sufficientaxial rigidity, the cross-section of the rods being dimensioned andconfigured so that the sum of the moments of inertia of the rods, insaid transversal direction is a fraction of the moment of inertia, insaid transversal direction, of a single-piece rod having a cross-sectionarea corresponding to the sum of the cross-section areas of the rod. 3.The driving rod as set forth in claim 2, wherein the sum of the momentsof inertia of the rods corresponds to a fraction “n” of the moment ofinertia of a single-piece driving rod with a cross-section areacorresponding to the sum of the cross-section areas of the rods.
 4. Thedriving rod as set forth in claim 2, wherein the sum of the moments ofinertia of the rods corresponds to a fraction “n2” of the moment ofinertia of a single-piece driving rod with a cross-section areacorresponding to the sum of the cross-section areas of rods.
 5. Thedriving rod as set forth in claim 2, wherein the rods are symmetricallydisposed around the displacement axis of the piston and laterally seatedto each other.
 6. The driving rod as set forth in claim 5, wherein therods are rectilinear and parallel to each other.
 7. The driving rod asset forth in claim 5, wherein the rods are disposed in a helicalarrangement.
 8. The driving rod as set forth in claim 5, wherein therods present a circular cross-section with equal flexibility in anytransversal direction.
 9. The driving rod as set forth in claim 5,wherein the rods are rectilinear, parallel and laterally seated to eachother, each rod having a rectangular cross-section with a dimensioncorresponding to a dimension (L) of the rectangular cross-section of asingle-piece driving rod, and with the other dimension (h) correspondingto the fraction “n” of the other dimension (H) of the cross-section ofsaid single-piece driving rod, the cross-section of the lattercorresponding to the sum of the cross-section areas of the “n” rods ofthe driving rod with multiple rods.
 10. The driving rod as set forth inclaim 2, wherein the rods are jointly and medianly surrounded by atleast one sleeve occupying part of the longitudinal extension of thedriving rod.
 11. The driving, rod as set forth in claim 10, wherein thesleeve is defined by an elastic ring pressing the rods against eachother.
 12. The driving rod as set forth in claim 10, wherein the sleeveis defined by a helical spring tightly mounted around the rods of thedriving rod.
 13. The driving rod as set forth in claim 10, wherein thesleeve is defined by a tube extension mounted with a small clearancearound the rods of the driving rod.
 14. The driving rod as set forth inclaim 2, wherein the rods present opposite ends defining the ends of thedriving rod, said rods having each of the opposite ends jointly affixedto a terminal block.
 15. The driving rod as set forth in claim 14,wherein each terminal block comprises a tubular body incorporating anenlarged end head turned to the rods and presenting, internally, ahousing axially defined through the enlarged end head and through atleast part of the extension of the tubular body.
 16. The driving rod asset forth in claim 15, wherein the tubular body is externally threaded,the enlarged end header being in the form of a hexagonal nut.
 17. Thedriving rod as set forth in claim 14, wherein the opposite ends of therods are laterally curved, defining an anchorage deformation, eachterminal block being rolled over one of the opposite ends of the rods.18. The driving rod as set forth in claim 17, in wherein each terminalblock comprises an elongated body incorporating an enlarged end headturned to the rods.
 19. The driving rod as set forth in claim 18,wherein the elongated body is externally threaded, the enlarged end headbeing in the form of a hexagonal nut.
 20. The driving rod as set forthin claim 14, wherein the terminal blocks are each formed by a pair ofplates to be affixed to each other, sandwiching a respective end of therods.
 21. The driving rod as set forth in claim 14, wherein the terminalblocks are defined by eyes of a driving rod in the form of a connectingrod of a reciprocating compressor.